Blind rivets are used to permanently join workpieces that are in contact with one another. The workpieces typically have holes passing through them that are brought into alignment with one another and into which the blind rivet is placed and then fastened by deformation. A fastened blind rivet results in a clearance-free seating in the holes of the workpieces and clamps the workpieces together. Normally, a blind rivet is never removed again. However, in cases in which repair of the joined parts is necessary or when a blind rivet has been set incorrectly, it is necessary to remove a blind rivet.
In the automotive industry, uses of blind rivets include fastening door module supports that are populated with attached parts such as power-window motors, loudspeakers, and other parts if applicable, to the door frame using multiple blind rivets. Failures of individual attached parts can make it necessary for doors to be disassembled and the door module supports to be removed. The blind rivets previously used must be drilled out for the disassembly. During this process, wandering of the drill can occur when the rivet mandrel is made of a relatively hard material, such as steel, and the rivet body is made of a relatively soft material, such as aluminum. Thus it is not uncommon for the door frame and also the module support to be damaged during the drilling-out process. The drilling chips and removed parts of the rivet fall to the ground or even into the blind area of the door, and can only be removed from the latter with extra effort. There is thus a need to create a blind rivet for these and other applications which can be released in a simple manner and can be removed in a single piece. In addition, the blind rivet must be simple to install and must join the workpieces firmly and permanently to one another after assembly.
A blind rivet that is intended to be removed in a single piece is known from EP 1,728,569 A1. In this blind rivet, which has a rivet body with a head designed as a flange and has a rivet mandrel passing through the rivet body, the rivet mandrel is shaped such that it can be pulled at least partially through the rivet body and out of the end of the rivet body opposite the flange during setting of the blind rivet. In addition, the flange is provided with a stepped region for the placement of a rivet removal tool, with the flange being dimensioned such that it does not deform or break when the rivet is withdrawn. In this blind rivet, the rivet body is made of plastically deformable metal and is dimensioned such that it projects only a short distance on the blind side of the workpieces. Accordingly, setting of the rivet forms only a comparatively small bead, which can be pressed together by a tensile force acting on the rivet body, in order to thus allow the blind rivet to be pulled from the holes in the workpieces. However, it is disadvantageous here that the holding forces of the blind rivet are very limited, and, like the release forces, are strongly dependent on manufacturing-related dimensional variations in the holes and the rivet parts.
In addition, from U.S. Pat. No. 4,238,446 which is a corresponding application to DE 29 06 250 A1 is known a plastic blind rivet with a mandrel having an expanded head and with a rivet body surrounding the mandrel, in which the mandrel has a series of engagement teeth on its outer circumference, and the inside wall surface of the rivet body has a series of anchor steps suitable for engaging the engagement teeth. The rivet body is provided with a flange-like head part and with an end that is inseparably joined to the mandrel head, and is deformed during setting of the blind rivet by partial withdrawal of the mandrel from the rivet body such that a part of the wall surface of the rivet body adjacent to the mandrel head is folded outward around the mandrel head and, together with the mandrel head, is pulled into the other part of the wall surface, with the latter bulging outward. In this process, the folded section of the wall surface is forced in between the mandrel head and the unfolded section of the wall surface, in which process the unfolded wall section must be stretched very severely. This requires relatively high forces for setting the blind rivet and results in severe stressing of the plastic material, restricting the choice of material. The prior art plastic blind rivet is not designed for easy removal of the set blind rivet.
According to WO 2011/113498 A1, which is an English equivalent of DE 10 2010 002847.9, the blind rivet has a hollow body made of plastic, which has an elongated shank that extends coaxially to a longitudinal center axis of the blind rivet and has a bore, a head extending radially at one end of the shank for contact with an accessible side of a workpiece and, at the opposite end, a foot end that is passed through an opening in the workpiece. Located in the rivet body is a mandrel that has a mandrel shank with a drawing end projecting out of the head of the rivet body and has a mandrel head that stands in operative connection with the foot end of the rivet body in order to transmit a force to the rivet body during setting of the blind rivet. The shank of the rivet body has, located between the head and the foot end, a first region with reduced cross-section and reduced wall thickness as compared to the regions adjoining the head and the foot end, wherein a second region with reduced cross-section and reduced wall thickness as compared to the first region is located within the first region in such a manner that, as a result of a process in which the head is pressed against one side of the workpiece and the foot end is simultaneously drawn toward the other side of the workpiece with the aid of the mandrel, the wall of the section of the first region located between the foot end and the second region forms a roll fold that on the outside rests against the section located between the head and the second region, and forms an annular bead pressed against the workpiece.
In the blind rivet according to WO 2011/113498 A1, which is an English equivalent of DE 10 2010 002847.9, during the fastening process the shank of the rivet body forms an annular bead on the blind side of the workpiece due to the folding; the annular bead surrounds a part of the shank adjoining the workpiece and rests against the edge region of the mounting hole surrounding the mounting hole in the workpiece. The annular bead is pressed firmly against the workpiece by the tensile force exerted on the mandrel that is transmitted by the mandrel head to the foot end of the folded shank. In this way, a strong axial contact pressure is achieved between the workpieces joined by the blind rivet, since the tensile force exerted during fastening of the rivet is transmitted directly to the workpiece without deflection, and the axial contact pressure need not be achieved through components of a force spreading the rivet shank apart. The blind rivet according to the invention further has the advantage that the annular bead of the folded shank resting against the blind side of the workpiece produces a good seal. This seal results not only from the strong contact pressure of the annular bead, but also profits from the fact that the annular bead works together with the edge of the workpiece surrounding the mounting hole at a distance from the mounting hole, so that damage or faulty formation of the hole edge cannot impair the seal. Even an eccentric position of the blind rivet with respect to the mounting hole is compensated by the larger diameter of the annular bead, and does not impair the seal action. In the fastened position, the mandrel is anchored in the shank of the blind rivet with the aid of locking means. In this way, the part of the shank extending from the foot end to the contact surface of the annular bead is loaded with the axial clamping force and experiences an elastic compression, and thus creates a spring action that counteracts vibratory loads and reduces effects on the clamping force caused by temperature changes.
In the blind rivet according to WO 2011/113498 A1, which is an English equivalent of DE 10 2010 002847.9, when the hollow rivet body made of plastic is primary molded, asymmetrical stresses can occur in the rivet body. These material stresses present in the rivet body after the fabrication process can lead to asymmetrical deformation of the rivet body during setting of the blind rivet and can impair a uniform contact of the annular bead with the workpiece.